This study is part of an NIH funded grant. It is designed to accomplish the following goals: 1) validate the safety and efficacy of pallidotomy in Parkinson disease, 2) better define the optimal target location, and 3) provide important data on the effects of pallidal lesions on motor, cognitive and psychiatric functioning in parkinsonian patients. A total of 84 patients are planned, and 25 have been entered and randomized to either medical or surgical treatment.